Vehicle creep control in a hybrid electric vehicle

Abstract

In a powertrain that includes wheels for driving a vehicle, an engine including a crankshaft, a machine driveably connected to the crankshaft and able to operate alternately as an electric motor and electric generator, a transmission including an input clutch driveably connected to the crankshaft and an output driveably connected to at least two of the wheels, and an electric storage battery having a variable state of charge and electrically connected to the machine, a method for controlling vehicle creep including adjusting a torque capacity of the input clutch to a desired magnitude of input clutch torque transmitted to the wheels, determining a desired change in torque produced by the machine such that a speed of the crankshaft is controlled to a desired idle speed, using the magnitude of input clutch torque capacity and the desired change in torque produced by the machine to determine a desired magnitude machine torque, and using the machine to produce said desired magnitude of machine torque.

1. A method for controlling vehicle creep, comprising:
 (a) using a crankshaft speed error to determine a change in electric machine torque that would produce a desired crankshaft idle speed; 
 (b) using a desired magnitude of input clutch torque capacity and said change in electric machine torque to determine a desired magnitude of electric machine torque; and 
 (c) using the desired electric machine torque to drive the vehicle. 
 
     
     
       2. The method of  claim 1  further including the step of using a battery to supply electric power to the machine. 
     
     
       3. The method of  claim 1  wherein step (a) further includes the steps of:
 determining a desired crankshaft idle speed; 
 determining an idle speed error from a difference between a current crankshaft idle speed and the desired crankshaft idle speed; and 
 determining the desired change in torque produced by the electric machine such that the idle speed error is minimized. 
 
     
     
       4. The method of  claim 1  further comprising the steps of:
 determining whether a battery state of charge is low or high relative to a reference state of charge; 
 if the battery state of charge is greater than the reference state of charge, using an electric machine to produce said desired magnitude of machine torque; 
 if the battery state of charge is less than the reference state of charge:
 using an engine to drive the machine; 
 using the machine to generate electric energy; and 
 storing in a battery electric energy produced by the machine. 
 
 
     
     
       5. The method of  claim 1  wherein step (a) further includes the step of using a speed of the vehicle and a position of a brake pedal to determine the desired magnitude of torque transmitted through a transmission input clutch. 
     
     
       6. The method of  claim 1  wherein step (a) further includes the step of using a speed of the vehicle and a brake system pressure to determine the desired magnitude of torque transmitted through a transmission input clutch. 
     
     
       7. In a vehicle powertrain, an engine including a crankshaft, a first machine driveably connected to the crankshaft and able to operate alternately as an electric motor and electric generator, a transmission including an input clutch driveably connected to the crankshaft and an output driveably connected to a first set of wheels, a second machine able to operate as an electric motor and driveably connected to a second set of wheels, and an electric storage battery having a variable state of charge and electrically connected to the first machine and second machines, a method for controlling vehicle creep, comprising the steps of:
 (a) using the second machine to produce torque and drive the second set of wheels after vehicle creep control begins; 
 (b) adjusting a torque capacity of the input clutch to a desired magnitude of input clutch torque transmitted to the first set of wheels during a vehicle creep condition; 
 (c) determining a desired change in torque produced by the first machine such that a speed of the crankshaft is controlled to a desired idle speed; 
 (d) using the magnitude of input clutch torque capacity and the desired change in torque produced by the first machine to determine a desired magnitude first machine torque; and 
 (e) decreasing torque produced by the second machine and using the first machine to produce said desired magnitude of first machine torque and the engine to drive the first set of wheels during the vehicle creep condition. 
 
     
     
       8. The method of  claim 7  further including using the battery to supply electric power to the machines. 
     
     
       9. The method of  claim 7  wherein step (c) further includes:
 determining a desired crankshaft idle speed; 
 determining an idle speed error from a difference between a current crankshaft idle speed and the desired crankshaft idle speed; and 
 determining the desired change in torque produced by the machine such that the idle speed error is minimized. 
 
     
     
       10. The method of  claim 7  further including the steps of:
 determining whether the state of charge is low or high relative to a reference state of charge; 
 if the state of charge is greater than the reference state of charge, using the first machine to produce said desired magnitude of first machine torque; 
 if the state of charge is less than the reference state of charge:
 using the engine to drive the first machine; 
 using the first machine to generate electric energy; and 
 storing in the battery electric energy produced by the first machine. 
 
 
     
     
       11. The method of  claim 7  further including the step of using a speed of the vehicle and a position of a brake pedal to determine the desired magnitude of torque transmitted through the input clutch. 
     
     
       12. The method of  claim 7  wherein step (b) further includes the step of using a speed of the vehicle and a brake system pressure to determine the desired magnitude of torque transmitted through the input clutch. 
     
     
       13. A system for controlling a powertrain during a vehicle creep condition comprising:
 wheels for driving the vehicle; 
 an engine including a crankshaft; 
 a machine driveably connected to the crankshaft and able to operate alternately as an electric motor and an electric generator; 
 a transmission including an input clutch driveably connected to the crankshaft, and an output driveably connected to the wheels; 
 an electric storage battery having a variable state of charge and electrically connected to the machine; and 
 a controller configured to use a crankshaft speed error to determine a change in electric machine torque that would produce a desired crankshaft idle speed, to use a desired magnitude of input clutch torque capacity and said change in electric machine torque to determine a desired magnitude of electric machine torque, and to cause the desired electric machine torque to drive the vehicle. 
 
     
     
       14. The system of  claim 13 , wherein the controller is further configured to use a battery to supply electric power to the machine. 
     
     
       15. The system of  claim 13  wherein the controller is further configured to determine a desired crankshaft idle speed, determine the idle speed error from a difference between a current crankshaft idle speed and the desired crankshaft idle speed, and determine the desired change in torque produced by the machine such that the idle speed error is minimized. 
     
     
       16. The system of  claim 13  wherein the controller is further configured to determine whether a battery state of charge is low or high relative to a reference state of charge; if said state of charge is greater than the reference state of charge, to use the machine to produce said desired magnitude of machine torque; if said state of charge is less than the reference state of charge, to use the engine to drive the machine; to use the machine to generate electric energy; and to store in the battery electric energy produced by the machine. 
     
     
       17. The system of  claim 13  wherein the controller is further configured to use a speed of the vehicle and a position of a brake pedal to determine the desired magnitude of torque transmitted through the input clutch. 
     
     
       18. The system of  claim 13  wherein the controller is further configured to use a speed of the vehicle and a brake system pressure to determine the desired magnitude of torque transmitted through the input clutch. 
     
     
       19. A system for controlling a powertrain during a vehicle creep condition comprising:
 first and second sets of wheels for driving the vehicle; 
 an engine including a crankshaft; 
 a first machine driveably connected to the crankshaft and able to operate alternately as an electric motor and an electric generator; 
 a transmission including an input clutch driveably connected to the crankshaft, and an output driveably connected to the first set of wheels; 
 a second machine able to operate as an electric motor and driveably connected to the second set of wheels; 
 an electric storage battery having a variable state of charge and electrically connected to the machines; and 
 a controller configured to use the second machine to produce torque and drive the second set of wheels after vehicle creep condition begins; to adjust a torque capacity of the input clutch to a desired magnitude of input clutch torque transmitted to the first set of wheels during the a vehicle creep condition; to determine a desired change in torque produced by the first machine such that a speed of the crankshaft is controlled to a desired idle speed; to use the magnitude of input clutch torque capacity and the desired change in torque produced by the machine to determine a desired magnitude machine torque; to decrease torque produced by the second machine, and to use the first machine to produce said desired magnitude of first machine torque and the engine to drive the first set of wheels during the vehicle creep condition. 
 
     
     
       20. The system of  claim 19 , wherein the controller is further configured to use the battery to supply electric power to the machines. 
     
     
       21. The system of  claim 19  wherein the controller is further configured to determine a desired crankshaft idle speed, determine an idle speed error from a difference between a current crankshaft idle speed and the desired crankshaft idle speed, and determine the desired change in torque produced by the machine such that the idle speed error is minimized. 
     
     
       22. The system of  claim 19  wherein the controller is further configured to determine whether the state of charge is low or high relative to a reference state of charge; if the state of charge is greater than the reference state of charge, to use the first machine to produce said desired magnitude of machine torque; if the state of charge is less than the reference state of charge, to use the engine to drive the machine, to use the first machine to generate electric energy, and to store in the battery electric energy produced by the first machine. 
     
     
       23. The system of  claim 19  wherein the controller is further configured to use a speed of the vehicle and a position of a brake pedal to determine the desired magnitude of torque transmitted through the input clutch. 
     
     
       24. The system of  claim 19  wherein the controller is further configured to use a speed of the vehicle and a brake system pressure to determine the desired magnitude of torque transmitted through the input clutch. 
     
     
       25. In a vehicle powertrain, an engine including a crankshaft, a first machine driveably connected to the crankshaft and able to operate alternately as an electric motor and electric generator, a transmission including an input clutch driveably connected to the crankshaft and an output driveably connected to a first set of wheels, a second machine able to operate as an electric motor and driveably connected to a second set of wheels, and an electric storage battery having a variable state of charge and electrically connected to the first machine, a method for controlling vehicle creep, comprising the steps of:
 (a) using the second machine to produce torque and drive the second set of wheels after vehicle creep control begins; 
 (b) adjusting a torque capacity of the input clutch to a desired magnitude of input clutch torque transmitted to the first set of wheels during a vehicle creep condition; 
 (c) determining a desired change in torque produced by the first machine such that a speed of the crankshaft is controlled to a desired idle speed; 
 (d) using the magnitude of input clutch torque capacity and the desired change in torque produced by the first machine to determine a desired magnitude first machine torque; and 
 (e) decreasing the torque capacity of the input clutch, decreasing the torque produced by the first machine, and increasing torque produced by the second machine to drive the vehicle wheels during the vehicle creep condition.